In some engine valve for automobiles or the like, a hollow part is provided and filled with metallic sodium to achieve a weight reduction and improve heat transfer efficiency of the engine valve in order for an engine to achieve a high performance, reduction of fuel consumption, or the like.
For such an engine valve, a manufacturing method has been proposed in which the head part is kept at a temperature high enough to melt metallic sodium while wire-shaped metallic sodium is sent into the hollow part through the opening at the upper end of the stem part, so that the metallic sodium is supplied while being liquefied in the hollow part, as described in the following Patent Literature 1, for example.
Besides the above, another manufacturing method has been proposed in which a nozzle is inserted to reach the hollow part of the head part through the opening at the upper end of the stem part, and molten metallic sodium is provided through the nozzle, so that the metallic sodium is injected into the hollow part, as described in the following Patent Literature 2, for example.